1. Field of the Invention
The present invention relates to an overcurrent preventing circuit, and more particularly to an overcurrent preventing circuit which, upon detection of an overcurrent, intercepts the shorted-out circuit.
2. Description of the Related Art
The connection terminals of the case for housing a battery are exposed so that they can be readily connected to their counterparts on the principal apparatus to which the battery supplies power. Therefore, if the connection terminals of the plus pole and the minus pole are accidentally short-circuited by coming into contact with an electroconductive object, a large current may flow in the shorted-out circuit, resulting in the overheating of the battery case. This might burn the user or even invite a fire. In view of this risk, various structures have been proposed to prevent short circuiting.
For instance, the Japanese Laid-Open Patent Application No. 53873/1988 (JP-A-63-53873) discloses a connecting terminal arrangement which connects, via relay terminals, connection terminals provided on a box, such as a battery case, to those of the principal apparatus to which the battery supplies power. This connecting terminal arrangement further has partitioning boards on both sides of the relay terminals. In this manner, when the box is separated from the principal apparatus, the partitioning boards prevent the connection terminals from coming into contact with each other even if an electroconductive object approaches the box.
The Japanese Laid-Open Utility Model Application No. 50447/1988 (JP-U-63-50447) discloses a structure to prevent short-circuiting by covering at least one of paired connection terminals when the battery case is not fitted to the principal apparatus to which the battery supplies power. Similarly, the Japanese Laid-Open Utility Model Application No. 62657/1990 (JP-U-02-62657) discloses a battery pack having a protective cover over the connection terminals.
Furthermore, the Japanese Laid-Open Utility Model Application No. 14361/1992 (JP-U-04-14361) discloses a short-circuit preventing apparatus having a lead switch within the power supply circuit of the battery box and a magnet within the principal apparatus to which the battery supplies power. This lead switch is usually kept open and is closed when the principal apparatus is fitted to the box, i.e. when magnetic force is given by the magnet.
Since all these examples of the prior art prevent the connection terminals from contacting each other by a mechanical structure, the two connecting terminals may become exposed if the contact preventing part is damaged or deformed. Therefore, accidental short-circuiting of the connection terminals cannot always be avoided.
Moreover, they require such extra parts as the relay terminals, protective cover and magnet, which make it necessary to provide a protruding part on the battery box. Furthermore, the magnet may affect internal circuits of the principal apparatus to which the battery supplies power.